Comparative Study of Emission from Highly Excited (In, Al) GaN Thin Films and Heterostructures
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Recently, nearly a dozen research groups have demonstrated lasing in InGaN-based heterostructures, with the lowest reported emission wavelength being 376 nm [2]. However, to obtain shorter wavelength laser diodes, it is necessary to use AlGaN-based structures. Preliminary studies have shown that the incorporation of Al into GaN increases the stimulated emission (SE) threshold [3]. In this work, we demonstrate that the introduction of strong optical and carrier confinement into AlGaN/GaN heterostructures can significantly reduce the SE threshold. We also demonstrate SE in AlGaN epilayers with emission wavelengths as low as 327 nm at room temperature, illustrating that AIGaN is a suitable material for the development of deep ultraviolet laser diodes. EXPERIMENT The GaN, InGaN, and AlGaN epilayers studied were grown on (0001) sapphire substrates by MOCVD. The thickness of the AlxGal-5 N layers were -0.8 ýtm, and had alloy concentrations of x = 0.17 and 0.26. For the purpose of comparison, we used GaN and InGaN epilayers with thicknesses ranging from 100 nm to 7.2 pm. The sample growth parameters have been reported elsewhere [4, 5]. We also studied an AIGaN/GaN separate confinement heterostructure (SCH) grown by MBE on 6H-SiC. The active region of the SCH was a 70 A thick GaN layer, which was sandwiched between a 600 A AI0.06Gao.94N cladding layer and a 2300 A Alo. 1IGao.89N 351 Mat. Res. Soc. Symp. Proc. Vol. 572 © 1999 Materials Research Society
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